Formation of a Tornado Explained: Collision of Warm, Moist Air & Cold Dry Air, Elevated Thunderheads, Rotation, Downdraft

CNN meteorologist Jennifer Gray explains how tornadoes form and why they are one of the most dangerous weather phenomena on Earth.

Scale Wind speed
Relative frequency Potential damage
mph km/h m/s
EF0 65–85 105–137 29–37 53.5% Minor or no damage.

Peels surface off some roofs; some damage to gutters or siding; branches broken off trees; shallow-rooted trees pushed over. Confirmed tornadoes with no reported damage (i.e., those that remain in open fields) are always rated EF0.
EF1 86–110 138–177 38–49 31.6% Moderate damage.

Roofs severely stripped; mobile homes overturned or badly damaged; loss of exterior doors; windows and other glass broken.
EF2 111–135 178–217 50–60 10.7% Considerable damage.

Roofs torn off well-constructed houses; foundations of frame homes shifted; mobile homes completely destroyed; large trees snapped or uprooted; light-object missiles generated; cars lifted off ground.
EF3 136–165 218–266 61–73 3.4% Severe damage.

Entire stories of well-constructed houses destroyed; severe damage to large buildings such as shopping malls; trains overturned; trees debarked; heavy cars lifted off the ground and thrown; structures with weak foundations are badly damaged.
EF4 166–200 267–322 74–90 0.7% Extreme damage.

Well-constructed and whole frame houses completely leveled; cars and other large objects thrown and small missiles generated.
EF5 >200 >322 >90 <0.1% Total destruction of buildings.

Strong framed, well built houses leveled off foundations and swept away; steel-reinforced concrete structures are critically damaged; tall buildings collapse or have severe structural deformations; some cars, trucks and train trucks can be thrown approximately 1 mile (1.6 kilometres).

Table modified from Wikipedia (“Enhanced Fujita Scale”).


Prairie Wind Chasers: 7-31-2011 Collis, MN EF-0 Tornado


EF-1 Tornado touchdown over Reinbeck, Iowa on July 7, 2014.


Yates City – Elmwood, Illinois EF2 Tornado June 5, 2010. This tornado started in an open field and damaged a barn and several power poles. Power flashes are visible. The tornado moves on to uproot a tree and throw the root ball hundreds of feet, scattering the soil in a puff of dirt. The tornado then moves north of Yates City where it does more damage to homes. The tornado did substantial damage to downtown Elmwood. No injuries were reported in this storm.


Footage of a developing EF3 tornado near Canton, Oklahoma. This tornado was documented during the May 24, 2011 Oklahoma tornado outbreak [NO AUDIO until 4:09 elapsed time].


WARNING GRAPHIC LANGUAGE: Rochelle/Hillcrest/Fairdale EF4 Tornado April 9, 2015.


A video summary of our storm chase through the El Reno area on May 31, 2013 featuring the 2.6 mile wide El Reno, OK EF5 tornado, and a smaller anticyclonic tornado. In memory of Carl Young, Paul and Tim Samaras. Music is courtesy Kevin MacLeod of

The El Reno area tornado killed four storm chasers, which are believed to be the first deaths in the history of storm chasing. The tornado moved over mostly open terrain, but dozens of storm chasers were unaware of its enormous size — possibly because the larger size rotation was more difficult to detect than a tighter vortex. About 12 storm chasers were caught off-guard. Along Highway 81, TWISTEX scientist and engineer Tim Samaras, his son Paul, and research partner Carl Young were killed by the tornado. Paul and Young were ejected from their Chevrolet Cobalt by the storm’s sub-vortex while Tim was still buckled in the passenger’s seat next to Young’s position, which was the driver’s seat. Local resident Richard Henderson, who decided to follow the storm, was killed nearby. His cellphone was found with a picture of the tornado. Other chasers, including well-known weather personalities Mike Bettes of The Weather Channel and Reed Timmer, were either injured or had their vehicles damaged. Reed Timmer was in Storm Research Vehicle SRV Dominator 2, which had its hood ripped off during the encounter with the tornado.

Last tweet by Tim Samaras on the day he was killed …

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